(1) Field of the Invention
This invention relates to an artificial respirator with two jet gas injection tubes which can afford a high efficiency of ventilation by high-frequency oscillation.
(2) Description of the Prior Art
As is well known, natural respiration or breathing is effected by inflating the lungs to maintain the pressure in the trachea and bronchi at a negative pressure to inspire air and by deflating the lungs to maintain the pressure in the trachea and bronchi at a positive pressure. Recently, a new artificial respiration method has been proposed and widely used in the medical fields. This method is referred to as a high-frequency oscillation (HFO) ventilation method in which a jet gas of auxiliary respiration gas is injected into the trachea and bronchi at a relatively high repetition frequency of 200 to 5000 cycles per minute so that the respiration gas in the lungs is stirred up to enhance the ventilation. Thus, the partial pressures of O.sub.2 and CO.sub.2 in the blood are kept to a proper level even during apnea.
One previously known such a respirator is shown illustratively in FIG. 1. In the figure, a respiration gas is generated in a gas mixer 1, gas sources 2 and 3 of oxygen and air being respectively coupled for feeding the gasses thereto. A proper amount of oxygen and air is introduced into the mixer 1 and then is mixed to produce a mixture gas for use in respiration.
The respiration gas thus produced is delivered through a communication tube 6 to a humidifier 7 where the respiration gas is made humid. After being humidified, the respiration gas is supplied through a communication tube 8 and further through an endotracheal cannula 11 into the lungs. The cannula 11 is coupled to the tube 8 by means of a T-fitting 10 at its one opening. In the midst of the path along the communication tube 8, a rebreathing bag 9 is provided so as to accumulate the respiration gas therein for supplying, when occasion demands, an additional gas to the lungs by squeezing it. The remaining opening of the T-fitting 10 opens into air by way of a communication tube 12 having a predetermined length. The tube 12 functions to impart resistance against the gas flow and hence to impart a small positive pressure to the respiration gas for use in the ventilation. In addition, the tube 12 is also used for the passage of the gas expiring from the lungs through the cannula 11 into air. At the vicinity of the cannula end, a cuff 11a is provided for blocking the intermediate flow passage between the airways and the outer surface of the cannula 11, thereby preventing a leakage of the respiration gas within the airways into air. However, it is not necessary to have the cuff 11a so long as a high-frequency oscillation method is employed because there is no substantial leakage of the respiration gas in such a method. In this case. the expired gas from the lungs can be expelled out into air through the intermediate passage and also through the cannula 11a and tube 12.
The respiration gas in the mixer 1 is also delivered to a high-frequency ventilation device 5 which is composed of a pneumatic circuit comprising fluidic devices. The fluidic devices operate to change the flow lines of the gas circuit in response to variations in the pressure of the gas. The gas thus controlled is transformed into a jet air having predetermined volume and high repetition frequency, e.g., 200 to 5000 cycles per minute. The jet gas is thereafter guided through a gas tube 13 into a jet gas injection tube 14 with a small diameter of about 1 mm, the tip of the injection tube 14 being inserted into the interior of the cannula 11 for feeding the jet gas thereinto.
The respiration gas to be transported through the humidifier 7, the rebreathing bag 9, and the T-fitting 10 into the lungs is subjected to high-frequency oscillations due to the presence of the jet gas. Therefore, an improved ventilation, commonly called as ventilation by high-frequency oscillations, can be performed effectively. In order to monitor the internal pressure in the airways and to prevent risk of a possible high pressure, a pressure gauge 15 is used, and its measuring guide tube 15a is inserted into the cannula 11 at the location downstream from the opening end of the jet gas injection tube 14.
The respirator of this design described above has been found not entirely satisfactory, however, and has many disadvantages as in the following;
(1) A sufficient supply of the respiration gas into the lungs can be retained by virtue of the injection of the jet gas from the injection tube 14. While on the other hand, since the expired gas from the lungs are left as it is without taking any positive measures to forcibly expel it out of the lungs, through the cannula 11 and the tube 12, the expired gas in the airways is liable to halt and linger within the airways. As a result, the increase of the internal pressure of the airways most likely occurs with the lapse of time, and there is a fear for effecting adverse effects upon a patient under artificial ventilation.
(2) The position where the internal pressure is measured is located at the vicinity of the downstream of the jet gas from the injection tube 14 so that a correct or practically useful pressure can not be obtained.
(3) A relatively large volume of the jet gas with a high pressure is supplied from the jet gas injection tube 14 during ventilation, so that it is very hard to humidify and heat the respiration gas as desired, particularly when the ventilation is carried out for a long time duration.
(4) Furthermore, anesthetic material can not be vaporized with a precise density if the vaporization is carried out under a high flow rate of more than 20 liters per minute and high pressure of 0.1 to 5 kg per cm.sup.2, of the respiration gas. This brings about a hardship that an anesthetic apparatus can not be easily equipped with the respirator. It is not practical for the respirator to prepare and implement additional complicated circuits enabling the attachement of the anesthetic apparatus to the respirator.